Light emitting diodes, or LEDs, have been widely implemented in electronic devices and applications, including LED display panels. With the increased use of LED display panels, smaller pitch LED display panels are increasingly used for large-area high-quality displays. Smaller LED pitch leads to a higher LED density so that a relative lower brightness in each individual LED is sufficient to achieve the same brightness level required by display panel design. Additionally, with the increased LED efficiency, a lower driving current can achieve the same brightness level. In LED driver design, the internal reference current, or bias, is proportional to the output current. In conventional LED driver designs, it may take a small reference current a long time to charge the internal node with a relatively large capacitance to the target level. This time delay reduces the LED PWM pulse width and affects the brightness level. In addition, variations in the internal node capacitance cause the PWM pulse width to vary among LED drivers. Therefore, methods and devices are needed to solve above-discussed problems.